Briefly, this invention has to do with a method of making a plug-in fuse assembly like that disclosed in U.S. Pat. No. 3,909,767, granted Sept. 30, 1975, and which preferably comprises a plug-in element including a plate-like body of fuse metal having a pair of spaced confronting terminal blade portions to be received by pressure clip terminals in a mounting panel, current carrying extensions at the inner end portions of the pair of terminal blade portions and a fuse link portion of reduced thickness interconnecting the current carrying extensions, and an insulating body, preferably a synthetic plastic housing, anchored between the current carrying extensions, with the pair of terminal blade portions thereof extending outwardly from the housing.
The preferred method of making such a plug-in fuse assembly comprises providing a blank of fuse metal which is blanked to form the pair of laterally spaced coplanar terminal blade portions current carrying extensions thereof and the interconnecting fuse link portion of reduced thickness. When the fuse link portion thereof is very fragile, the blanking operation leaves a relatively rigid web between the terminal blade portions formed in the blank.
The synthetic plastic housing is then inserted over said blank of fuse metal so it terminates short of the transverse web and the blank of fuse metal is suitably secured in the synthetic plastic housing as by staking or other means so that it acts as a rigid insulating body connected between the current-carrying extensions and/or terminal blade portions of the partially enclosed plug-in fuse element. (While less desirable, the housing function for this body of insulation material can be eliminated so it acts only as a rigid support and, if desired, a convenient gripping surface for the plug-in fuse element.) Where used, the exposed transverse web of fuse metal interconnecting the exposed terminal balde portions of the blank is then blaked or otherwise removed to complete the formation of a housed plug-in fuse element whose exposed pair of terminal blade portions may be inserted into metal sockets or the like of a terminal strip.
For maximum mass production efficiency of the housed plug-in fuse element just described, the blank of fuse metal from which each plug-in fuse element is formed as preferably part of a long strip of fuse metal upon which various blanking operations are performed as the strip moves past various stamping stations. The individual plug-in fuse elements are not completely separated from the strip until just before or after the housing is applied thereto at the end of the strip.
One of the cost saving and size reducing aspects of the preferred method of making plug-in fuses just described is that each plug-in fuse element is a stamping made from a blank or strip of fuse metal, and a completely housed fuse results from merely enclosing the same in an insulating housing, so that the entire fuse assembly is formed of only two parts, and without any soldering operations required to connect a fuse link between the terminal portion of the fuse. The manufacturing costs are reduced to a minimum when various blanks form interconnected portions of a strip of fuse metal so that the strip acts as a carrier for the blanks as they are successively moved past stamping dies which carry out the blanking operations just described.
As disclosed in the aforementioned U.S. Pat. No. 3,909,767 and in the method of the aforementioned U.S. Pat. No. 3,962,782, the reduced thickness of the interconnecting fuse link portion is provided by initially milling and squeezing the blank of fuse metal only at a point in the blank where the interconnecting fuse-forming link portion is formed by the subsequent blanking operation. This requires a separate milling and squeezing operation at a precise point in each blank of fuse metal. With this procedure it is extremely difficult to maintain sufficiently accurate tolerances for the reduced thickness of the fuse-forming link portion of the plug-in element, and this is compounded where the blanks form integral parts of a continuous intermittently advanced strip of fuse metal, wherein deviations in reduced thickness can also occur from blank to blank, all of which is detrimental to mass porduction of plug-in fuse assemblies having accurate fuse ratings. In addition to this problem of maintaining tolerances and accurate fuse ratings there is also the problem of time consumption and cost in such procedure.
In the method of the instant invention, the aforesaid milling and squeezing operation at precise points in each blank and the aforementioned problems involved therewith are eliminated. In the method of this invention, the blank of fuse metal is initially provided with a continuous portion of reduced thickness extending between opposite margins thereof so that, when the blank is blanked, the interconnecting fuse-forming link portion of the blank is of less thickness than the spaced coplanar terminal blade portions and the current carrying extensions. Preferably, a continuous strip of fuse metal is utilized which is initially longitudinally provided throughout its length with a continuous longitudinal hard portion of reduced thickness. This band of reduced thickness in the blank or strip most advantageously passes through the center thereof so that by blanking the reduced thickness portion of the blank or strip there is left on opposite sides thereof said terminal blade portions and current-carrying extensions. (However, in accordance with the broadest aspects of the method invention disclosed in said patents, in the form of the invention where blanks are interconnected in a strip, the blanking operation may be carried out so that the terminal blade portions and current carrying extensions are oriented transversely rather than longitudinally of the strip and are formed on the same side of the band of reduced thickness, in which event the band of reduced thickness could extend along one margin of the strip or off-centered thereon.) The assembly of a housing on the strip is probably made easier by the method where the band of reduced thickness extends centrally of the strip and is blanked so that the terminal blade portions and their extensions are oriented longitudinally of the strip because a housing having an entry opening at one end can be readily slipped over an exposed longitudinally facing end of an end blank of the strip, either before or after it is reversed therefrom, to encompass the portion of the blank other than the terminal blade portion thereof which are to project from the housing. Also, when the band of reduced thickness is located within the longitudinal margins rather than along one margin of the strip or blank, the ends of the current carrying extensions formed from each blank are, like the terminal blade portions thereof, formed by the thicker portions of the blank where they can more readily withstand the pressure of testing probes without damage thereto.
The continuous portion of reduced thickness is preferably provided in the blank or continuous strip of fuse metal by controlled conventional continuous milling and scarfing procedures, whereby the tolerance of the portion of reduced thickness is kept within close limits. As a result, the thickness of the fuse-forming link portions of reduced thickness subsequently blanked from each blank is maintained within close tolerances, not only in each plug-in fuse element, but, also, from plug-in fuse element to plug-in fuse element blanked from the blank or continuous strip.
The portions of reduced thickness of the strip or blank of fuse metal may be formed by milling and scarfing both sides thereof or by milling and scarfing only one side thereof. The strip or blank of fuse metal may also be plated, such as tin plated, to provide improved electrical contact of the coplanar terminal forming blade portions of the ultimate plug-in element with the pressure clip terminals in the mounting panel in which they are received.
Other features and advantages of this invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawings.